1. Field of the Invention
The present invention relates to a method and apparatus for the continuous preparation of heated water flow for use in hydraulic fracturing.
2. General Background of the Invention In connection with production of oil or gas from a geological formation, the production may have a poor flow rate due to low permeability or from damage or clogging of the formation during drilling particularly in formations of tight sands with low porosity and oil & gas shales. Hydraulic fracturing also known as “fracing” is a process employed after the well has been drilled, for the completion of the well to enhance hydrocarbon production.
Hydraulic fracturing creates porosity by fracturing the formations surrounding the wellbore. These fractures allow the oil or gas to flow more easily from the tight sands or shales to the production well. The common method to create fractures in the formation is to pump a mixture of water, chemicals and sands into the rock or formation. When the pumped fluid mixture reaches sufficient pressures, the formation will fracture, creating the permeability required to release the captured hydrocarbons.
Hydraulic fracturing generally entails injecting fluid into the wellbore at a sufficient rate and pressure to overcome the tensile strength of the formation creating cracks or fractures extending from the wellbore. U.S. Pat. Nos. 3,816,151, 3,938,594 and 4,137,182 (each hereby incorporated herein by reference) relate to hydraulic fracturing processes using various fracturing fluids.
Also incorporated herein by reference are the following US Patent document no: 2008/0029267; U.S. Pat. Nos. 5,979,549; 5,586,720; 5,183,029; 5,038,853; 4,518,568; 4,076,628; 2,631,017; 2,486,141; 2,395,258; 2,122,900; 2,065,789.
One of the key elements of the fracturing fluid is water, which is the carrying fluid for the proppant (and optional appropriate chemical mix) required for the process. The proppant holds open the fractures and provides porosity to allow hydrocarbons to flow out of the formation. Before the fracing fluid is injected into the well, the water is normally heated to the target temperature (e.g., 40° F. to 120° F.+ (4.4° C. to 48.9° C.+)), which depends on the geologic formation and chemicals used, for example, typically 65° F.-75° F. (18° C.-24° C.) in the Bakken Shale located in North Dakota, Montana, and southern Canada) in order to achieve the proper chemical mix required for each particular hydraulic fracturing operation. A further result of heating the water prior to mixing with chemicals is the reduction of amount of chemicals that may be required for the hydraulic fracturing operation. In addition, a lower density of the heated water reduces the pressure on the pipes and connections and thereby reduces the risk for mechanical failure. In colder months and in colder environments, the temperature of the available water sources are typically less than 50° F. (10° C.) (even as low as below freezing) which is generally an unsuitably cold temperature for the fracing process. It is necessary to heat the available water to a temperature (e.g., 40° F. to 120° F.+ (4.4° C. to 48.9° C.+)) suitable for the fracing process prior to the water and fracing fluids being pumped down hole.
There are common and known methods of providing heated water, which require that prior to the fracing process, the source water is pumped into numerous frac tanks and then the water in each individual frac tank is circulated through a heating unit to raise the temperature in the frac tank to a preset temperature required for the chemical mixing of the frac. However, due to the time lapse between heating (which is typically done the night before the fracing operations) significant thermal loss occurs. Each tank has to be heated to temperatures of for example 10-50° F. (5.6° C. to 27.8° C.) (often 20° F. to 30° F. (−11.1° C. to 16.7° C.)) higher than is operationally necessary. For example, if the required temp is 70° F. (21° C.), then each tank would need to be heated to at least 90°-120° F. (32° C.-48.9° C.). The extensive over-heating is a substantial expense and energy waste. The pumping of water to the frac tanks and the use of heating units to heat the water in the frac tank are well known in the industry. FIG. 5 is an example of a prior art type configuration. There are multiple commercial businesses which provide such services. The number of frac tanks can typically range from 20-700 tanks (the average at the Marcellus Shale (located in western New York extending south to Tennessee) is 500 tanks)—currently it costs around $500-2,000 per frac tank in a typical fracing process (delivery, rental, cleaning, and demobilization of the tank), so these frac tanks are a substantial expense in the fracing process. Typically a substantial amount of safety issues in fracing operations involves the handling of frac tanks. One must heat the frac tanks to enough above the target temperature to allow for thermal loss between heating and use.
Because normally heating of frac tanks occurs at night, this can be 10-50 degrees F. (5.6° C. to 27.8° C.), for example. The amount of temperature above target will depend on local weather conditions.